The present invention relates to a metal hydride tank apparatus used for the hydrogen consuming apparatus such as fuel cells or hydrogen engines as a hydrogen supplier and more particularly relates to a metal hydride tank apparatus capable of efficiently discharging hydrogen gas, which is stored in the metal hydride in a tank, from throughout the metal hydride.
In recent years, electric vehicles of various types, on which a traction motor instead of a conventional engine is mounted, have been developed. As one of these electric vehicles, fuel cell electric vehicles, which employ a fuel cell as a power supply for the traction motor, are being rapidly developed. The fuel cell generates electric power by an electrochemical reaction of hydrogen and oxygen in the air. The fuel cell includes an air supply apparatus for the continuous compressed air supply, an air discharging apparatus for discharging residual air, a hydrogen gas supplying apparatus for the continuous hydrogen gas supply, a hydrogen gas discharging apparatus for discharging and recirculating the residual hydrogen gas to the hydrogen gas supplying apparatus, and cooling apparatus for keeping the temperature of fuel cell within an appropriate range, which make up a fuel cell system to allow the fuel cell to generate electric power continuously.
In the hydrogen gas supplying apparatus in the fuel cell system, a reformer which generates hydrogen gas from a liquid fuel like methanol etc. containing hydrogen and a high pressure hydrogen tank storing highly pressurized hydrogen gas are normally provided as a hydrogen gas supplier. Also, a metal hydride tank is provided, which is capable of storing hydrogen gas in a low-pressure condition compared with a high pressure hydrogen tank. The metal hydride tank apparatus is composed of a metallic tank made of aluminum or stainless steel etc., which contains a metal hydride. The metal hydride tank apparatus is capable of storing hydrogen gas with the more compact tank compared with a high-pressure hydrogen tank.
The metal hydride contained in the metal hydride tank apparatus stores the hydrogen gas flowing into the tank with exothermic reaction and discharges the stored hydrogen gas with endothermic reaction. The metal hydride will promote the exothermic reaction to continue storing the hydrogen gas when the metal hydride is cooled, on the other hand the metal hydride will promote the endothermic reaction to continue discharging the hydrogen gas when the metal hydride is heated. So in this type of metal hydride tank apparatus, as a means for the control of storing or discharging the hydrogen gas by heating or cooling the metal hydride, a heating medium channel, for example, is provided in the tank (Japan Laid-Open Patents 11-60201, 2000-170998 and 2000-120996).
The metal hydride expands or contracts the volume of the metal hydride when the metal hydride stores or discharges the hydrogen gas, the repetition of which will make the particle of the metal hydride finer and degrade the thermal conduction of the metal hydride. The prior metal hydride tank apparatus, which merely has a heating medium channel in the tank, has difficulty in heating the whole metal hydride rapidly due to the degradation of thermal conduction, giving rise to the problem that the metal hydride cannot discharge the hydrogen gas efficiently and rapidly from throughout the metal hydride.
Therefore, the object of the present invention is to provide an efficient metal hydride tank apparatus capable of discharging the hydrogen gas stored in the metal hydride in the tank efficiently and rapidly from throughout the metal hydride.
The present invention to address the above issues provides a metal hydride tank apparatus containing a metal hydride, wherein a temperature controllable tank comprising; a metal hydride, which discharges the stored hydrogen gas according to the temperature control of the tank; a gas channel, which discharges the hydrogen gas, discharged from the metal hydride, out of the tank; a baffle, which is placed in the tank and forms the gas channel into sections to flow the hydrogen gas throughout the metal hydride in the tank and discharge the hydrogen gas out of the tank.
In the metal hydride tank apparatus according to the present invention, the metal hydride will store the hydrogen gas with exothermic reaction when the hydrogen gas comes into the tank. If the tank is temperature controlled to cool the metal hydride, the metal hydride will promote the exothermic reaction and continue storing the hydrogen gas coming into the tank. If the tank is temperature controlled to heat the metal hydride thereafter, the metal hydride will promote the endothermic reaction and continue discharging the stored hydrogen gas. Then, the hydrogen gas discharged from the metal hydride will be discharged out of the tank, flowing through the hydrogen gas channel formed into sections with baffles in the tank. In the process of the hydrogen gas discharge, the metal hydride contained near the inner circumferential wall of the tank absorbs heats from the temperature raised tank and initiates discharging. The hydrogen gas discharged near the inner circumferential wall of the tank flows along the inner circumferential wall of the tank rapidly and absorbs heats from the inner circumferential wall of the tank efficiently. Further the hydrogen gas flows throughout the metal hydride in the tank to heat up the metal hydride rapidly, thus discharging the hydrogen gas efficiently from throughout the metal hydride.
In the metal hydride tank according to the invention, the baffles may be of a cylinder-like shape placed in the longitudinal direction of the tank or of a spiral-like shape in the cross section normal to the longitudinal direction of the tank. Also in the Metal hydride tank apparatus according to the invention, when the honeycomb structured holder containing the metal hydride is housed so that the longitudinal direction of the holder lies in that of the tank, the baffle is placed at both ends of the holder to form the hydrogen gas flow channel into sections in the holder.
The baffles should preferably be made of a hydrogen impermeable material so that the hydrogen gas discharged from the metal hydride may flow along the hydrogen gas channel reliably. Further, the baffles should preferably be made of an elastic material so that they may be held by the inner circumferential wall of the tank with elastic contact to the inner circumferential wall of the tank.